This proposal responds to research topic 12 (Cognition in Context), with secondary relevance to topic 19 (Genetics, Behavior and Aging). The aging of the U.S. population has stimulated public health interest in identifying factors that can preserve the cognitive functioning of older adults. Complex work may be one activity that has a salutary effect on late-life cognitive function, but factors like intelligence, educational level, and early environmental exposures are potential confounds to this association. Twin studies allow for control of many of these confounding factors. The goal of this project is to determine whether occupational complexity is associated with better late-life cognitive functioning in a sample of elderly twins, using data collected by the Duke Twins Study of Memory in Aging on members of the National Research Council-National Academy of Sciences (NAS-NRC) Registry of World War II veteran twins. Specific Aim 1 of this project is to classify each twin's primary lifetime occupation using the Dictionary of Occupational Titles (DOT), from which a measure of complexity can be derived. This allows additional Specific Aims (SA) to be tested using co-twin control analyses: (SA 2) estimate the association between occupational complexity and cognitive status, (SA 3) estimate the association between occupational complexity and change in cognitive status over time, and (SA 4) estimate the extent to which intelligence moderates the relationship between occupational complexity and cognitive status. The study sample, which comprises approximately 1000 monozygotic and 1000 dizygotic twin pairs, has been administered a cognitive status examination every 3-4 years since 1990 as part of a screening and assessment protocol for dementia. Approximately 300 of these pairs also have scores on standard armed services intelligence tests. Logistic regression dependent on twin pair will be used to estimate association between a factor-based measure of occupational complexity from the DOT and either baseline (SA 2) or change scores (SA 3) from the cognitive status measure. Analyses for SA 4 will be similar, using the intelligence test score as a covariate. If occupational complexity is found to enhance late-life cognitive functioning, this modifiable factor could inform cognitive interventions and influence decisions about occupational activities and retirement. Follow-up twin studies can explore whether complex work is a protective factor for dementia.